Key switch assembly for a computer keyboard

Abstract

A key switch assembly includes a base board, a membrane circuit provided on the base board, an upright biasing member supported on the membrane circuit, a base plate, a scissors-type key cap support including first and second support levers, and a key cap. The first support lever is formed with an aligned pair of cylindrical outward pins. The second support lever includes parallel rods that are formed with an aligned pair of pin bores with downwardly opening entrances to permit extension of the outward pins fittingly and rotatably therein via the entrances so as to couple rotatably the first and second support levers at intermediate portions of the same. The second support lever is further formed with an engaging tab on the inner edge of one of the parallel rods. The first support lever is further formed with an engaging notch on one of the outer edges of the first support lever for receiving the engaging tab therein. The engaging notch has a predetermined width sufficient to limit pivoting movement of the engaging tab therein between a first position, where the key cap is in a non-depressed state, and a second position, where the key cap is in a fully depressed state.

I claim: 
     
       1. A key switch assembly for a computer keyboard, said key switch assembly comprising: a base board;   a membrane circuit provided on said base board, said membrane circuit having an electrical contact;   an upright biasing member supported on said membrane circuit;   a base plate disposed on said membrane circuit and formed with an opening to permit extension of said biasing member therethrough, said opening having opposite first and second sides, said base plate being further formed with a first slot retainer unit adjacent to said first side of said opening, and a first pivot retainer unit adjacent to said second side of said opening;   a scissors-type key cap support including first and second support levers with upper and lower portions, and intermediate portions that are coupled rotatably about a pivot axis, said lower portion of said first support lever being retained pivotally in said first pivot retainer unit of said base plate, said lower portion of said second support lever being retained slidably in said first slot retainer unit of said base plate; and   a key cap having a bottom side formed with a second slot retainer unit for retaining slidably said upper portion of said first support lever, and a second pivot retainer unit for retaining pivotally said upper portion of said second support lever, said key cap being biased upwardly by said biasing member and being capable of being pressed so as to compress said biasing member and enable said membrane circuit to produce an electrical signal;   said first support lever having a generally U-shaped frame section with upper and lower sides and opposite outer edges, said intermediate portion of said first support lever being formed with an aligned pair of cylindrical outward pins disposed respectively on said outer edges of said first support lever;   said second support lever being formed as a generally U-shaped frame which includes parallel rods that flank said outer edges of said first support lever, and a transverse rod that interconnects said parallel rods at said upper portion of said second support lever, each of said parallel rods having upper and lower sides and an inner edge, said intermediate portion of said second support lever being formed with an aligned pair of pin bores disposed respectively on said inner edges of said parallel rods, each of said pin bores being formed with an entrance that opens to said lower side of the respective one of said parallel rods, said outward pins on said first support lever extending fittingly and rotatably into a respective one of said pin bores via said entrance so as to couple rotatably said intermediate portions of said first and second support levers;   said intermediate portion of said second support lever being further formed with an engaging tab which is disposed on said inner edge of one of said parallel rods adjacent to said pin bore and which extends between said upper and lower sides of said one of said parallel rods;   said intermediate portion of said first support lever being further formed with an engaging notch which is disposed on one of said outer edges of said first support lever adjacent to said outward pin and which extends from said upper side to said lower side of said first support lever, said engaging notch receiving said engaging tab therein and having a predetermined width sufficient to limit pivoting movement of said engaging tab therein between a first position, where said key cap is in a non-depressed state, and a second position, where said key cap is in a fully depressed state.   
     
     
       2. The key switch assembly of claim 1, wherein said engaging notch has a constricted intermediate section and opposite diverging end sections which open to a respective one of said upper and lower sides of said first support lever, each of said diverging end sections having a maximum width equal to said predetermined width, said constricted intermediate section having a width equal to thickness of said engaging tab. 
     
     
       3. The key switch assembly of claim 2, wherein said engaging notch is confined by opposite angled first and second walls, said first wall having first upper and first lower wall sections, said second wall having second upper and second lower wall sections, said engaging tab having opposite side faces that abut against said first lower wall section and said second upper wall section when said engaging tab is in the first position, and that abut against said first upper wall section and said second lower wall section when said engaging tab is in the second position. 
     
     
       4. The key switch assembly of claim 3, wherein said opposite side faces of said engaging tab are parallel to each other, said first lower wall section being parallel to said second upper wall section, said first upper wall section being parallel to said second lower wall section. 
     
     
       5. The key switch assembly of claim 1, wherein said entrance of each of said pin bores diverges in a direction away from said pin bore to facilitate fitting of the respective one of said outward pins in said pin bore. 
     
     
       6. The key switch assembly of claim 1, wherein said base plate includes: a hollow rectangular key confining frame portion;   aligned first and second hole defining portions extending inwardly from said frame portion and having terminating edges that confine said first and second sides of said opening; and   opposite flange units extending inwardly from said frame portion toward a respective one of two opposite longitudinal edges of said first hole defining portion so as to form two L-shaped slots within said frame portion at said two opposite longitudinal edges of said first hole defining portion, said L-shaped slots constituting said first slot retainer unit and having said lower portion of said second support lever extending slidably therein, said flange units having bottom surfaces which cooperate with said membrane circuit to form slide recesses therebetween.   
     
     
       7. The key switch assembly of claim 6, wherein said lower portion of said second support lever is formed with opposite outward slide shafts which are inserted into said L-shaped slots and which abut slidably against said bottom surfaces of said flange units for slidable retention in said slide recesses. 
     
     
       8. The key switch assembly of claim 7, wherein each of said flange units has an inclined top surface which inclines downwardly in a direction toward said slot units, each of said outward slide shafts being resilient and tapering in a direction away from a respective one of said parallel rods to form an inclined bottom surface that complements said inclined top surface on a respective one of said flange units so as to facilitate insertion of said outward slide shafts into said L-shaped slots. 
     
     
       9. The key switch assembly of claim 7, wherein said first hole defining portion has a top surface that is indented with respect to a top surface of said frame portion, said lower portion of said second support lever being further formed with opposite inward slide shafts which abut slidably against said top surface of said first hole defining portion. 
     
     
       10. The key switch assembly of claim 7, wherein said second hole defining portion is formed with opposite cantilevers which extend away from a respective one of two opposite longitudinal edges thereof, and opposite barb projections formed on said opposite longitudinal edges of said second hole defining portion and aligned spacedly and respectively with said cantilevers, said cantilevers and said barb projections constituting said first pivot retainer unit. 
     
     
       11. The key switch assembly of claim 10, wherein said lower portion of said first support lever is formed with opposite outward pivot shafts forced between aligned ones of said cantilevers and said barb projections for pivotal retention thereat. 
     
     
       12. The key switch assembly of claim 11, wherein the aligned ones of said cantilevers and said barb projections have top edges that form a converging entrance to facilitate forcing of said outward pivot shafts therebetween. 
     
     
       13. The key switch assembly of claim 11, wherein said cantilevers form clearances with said frame portion to enhance resiliency of said cantilevers.